Skip to main content

Full text of "Leguminous plants as organic fertilizers in California agriculture"

See other formats




December, 1922 



Legume Trial Garden at Berkeley, 1922 


This circular is intended as an introduction to a series of circulars 
dealing with leguminous crops suitable for growing under the con- 
ditions which prevail in California. 

The arable lands, orchard and grain, have been slowly but surely 
becoming less fertile with a steady decline in crop yields. This ex- 
ploitation of soil fertility by the removal of the crop, the burning 
out of the organic matter, and the leaching out of the nutritive prop- 
erties of the soil deserves serious consideration from the urban as 
well as the rural population of every community. 


The change from horse power to motor power, together with the 
low rate of growth of the animal industries as compared with the 
plant industries, leaves little to be expected from animal manures, 
the demand being far greater than the supply. Our attention there- 
fore turns to the vegetable manures as being the safest, surest, and 
most economical solution of the soil fertility problem. The utilization 
of legumes as green manure crops will go far toward restoring and 
maintaining soil fertility. No system of farming should be con- 
sidered rational that does not include a liberal use of legumes, which 
add to the nitrogen content of the soil instead of depleting it. Nitro- 
gen is one of the most essential elements for plant growth as well as 
the most expensive to maintain. It is readily leached out by rains 
and irrigation so that it must be constantly renewed. It is therefore 
especially necessary to consider at all times in farming opera- 
tions how this important element may be most economically in- 
troduced into the soil. The fact that it is possible by means of le- 
gumes to utilize the atmospheric nitrogen, so abundant and free to 
all, makes the importance of the subject apparent. 

The Legume Bacteria. — The legume organism, to which this fact 
is due, is very active in certain stages of its development, and gains 
entrance to the root mainly through the tip of the root hairs. This 
is probably accomplished by the aid of an enzyme which dissolves 
the cell wall. Multiplication by division from one to thousands takes 
place in a short time. The numerous bacteria produced incite the 
plant cells in the root to form a growth which we term a nodule. A 
specific type of organism and nodule occurs in each group of related 
legumes. Within certain limits these bacteria are interchangeable. 
To illustrate: the bacteria of sweet clover, bitter clover, bur-clover, 
-and alfalfa are interchangeable for purposes of inoculation, so that 
if a field which has been growing a good crop of bur-clover is to be 
planted to alfalfa there would be no necessity for inoculating the 
seed or soil artificially. Other legumes that have a sympathetic 
relationship with regard to their legume organisms are peas, len- 
tils, vetches, horse beans and sweet peas, while soy beans are not 
benefited by the organisms of any other group. The true clovers, 
red, alsike, crimson, white Dutch, and Egyptian or berseem, form 
another group. Still another group in which the bacteria are inter- 
changeable comprises cowpeas, velvet beans, peanuts and Japan 
clover. Lupines which occur so abundantly in California are probably 
of no value for inoculating the soil with bacteria for any of our 
common garden, field, or cover crops. So that much depends upon 

Circular 255] leguminous plants as organic fertilizers 3 

whether a legume of any kind has been growing in the soil, and if 
that particular legume will associate from an inoculation point of view 
with the one we wish to plant. 

Leguminous Plants. — To give an idea of the number and varia- 
bility of leguminous plants we may say that there are about 6500 
species belonging to the family, or 10,000 or more kinds if we include 
the different strains of garden and field peas and beans. They are 
widely distributed in all countries, but most abundantly in the 
tropics. Many of them are well known, such as alfalfa, sweet clover, 
bitter clover, red, crimson, alsike, and white Dutch clover, bur-clovers, 
lupines, sweet peas, vetches, velvet beans, soy beans, and peanuts. 
Others not so well known are the Spanish clovers, horse beans, fenu- 
greek, mung beans, jack beans, sword beans, lentils, grass peas, gar- 
banzos, kudzu, carob beans, seradella, sulla, guar, berseem, Tangier 
pea, Scotch broom, furze, mesquite beans, Japan clover, sainfoin, 
sesbania, sunn hemp, and hyacinth bean. Numerous additional species 
occur as native plants furnishing much wild forage in our valleys and 
mountains. There are a host of leguminous trees, shrubs, herbs, 
and climbing plants that are valuable mainly for shade and orna- 
mental purposes. 

The problem then, is to determine which of these legumes will 
grow satisfactorily in a given region. The purpose for which the 
legume is to be grown, whether for hay, pasture, soiling, silage, cover 
crop, or green manure, must be considered, and having decided this a 
study must be made of the climate, precipitation, and soil conditions, 
and whether the crop is to be grown with or without irrigation. 


Nearly all legumes require for their best growth a well-drained 
soil. Some of them respond to applications of lime or sulfur, 
or both. They will grow on a great many types of soil, from 
stiff clays to light sands, but prefer good loams. Few of them are 
tolerant of alkali even in small amounts. 


It has been stated again and again that our California soils need 
humus more than anything else. By humus is meant the organic 
matter in the soil in process of decomposition. The long hot summers 
have a tendency to burn out this organic matter, bringing about a 
poor physical condition. Hence, the advantage of a crop to cover 
the soil during the hottest part of the summer or, what we term, a 
cover crop. When the winter or summer legume is plowed under it 


forms humus which will transform stiff soils that are hard to work 
into friable loams. If the soil is sandy and inclined to be porous 
and leachy the addition of humus will change its physical condition 
so that it will be more retentive of moisture, less inclined to leach, 
and less liable to be blown about by the wind. Humus also affects 
the temperature of a soil in a beneficial manner by diminishing ex- 
tremes, so that it makes a soil cooler in summer and warmer in 
winter. Very few soils in California are in danger of having such 
an excess of humus that they would be too retentive of moisture, thus 
excluding the air, and bringing about putrefaction instead of the 
useful decomposition of the organic matter. The plowing-under of 
legumes to improve the physical condition of the soil is as important 
as the contribution of plant food which they make. One of the most 
important functions of humus is to make the soil habitable for the 
micro-organisms or bacterial flora which play such a large part in 
the formation of plant food. The mere fact of mineral nitrogen, 
phosphorus and potash being in the soil, is not sufficient, for with- 
out humus these do not make a fit habitat for the growing plant. A 
soil may be considered good from an agricultural standpoint if it 
contains from one to two per cent of humus. The temperature of the 
soil has an important bearing on the availability of the plant food. 
Nitrification takes place to a slight extent at 40° F. and increases 
up to 99° F. Above that it diminishes again and stops altogether 
at 130° F. It is necessary, therefore, not only to plow under the 
legume, but to have the proper conditions of moisture and tempera- 
ture to decompose it before it can feed the crop. 

The choice of a green-manure crop should be based on the avail- 
able water supply, both for the growing of the crop and for its de- 
composition when turned under. Applications of " strawy ' ' barn- 
yard manure have been made where the land was not irrigated that 
were harmful rather than beneficial, as the material did not decay 
but left air spaces, thus causing an additional loss of moisture at the 
most critical time. 


So much attention has been drawn to the nodules on the roots of 
legumes as " nitrogen gatherers" that their nitrogen value when com- 
pared with the nitrogen in the total plant has been over-rated. It is 
true that the nodules are very rich in nitrogen, some of them as high 
as 7.25 per cent, and that it is probably in a form directly available 
as plant food, while the root itself has only one to three per cent of 
nitrogen. The weight of the nodules, however, is but a small fraction 


of the total root, so that in most instances the roots contain less nitro- 
gen than the tops. Alfalfa and red clover have their nitrogen more 
equally divided between the roots and the tops. The former because 
of its extensive root system and the latter because of its numerous 
fine roots which are abundantly noduled. Analyses reported by the 
Delaware Agricultural Experiment Station, Bulletin No. 60, 1903, 
have shown 58 per cent of the nitrogen of the alfalfa in the tops and 
42 per cent in the roots and 68 per cent in the tops and 32 per cent in 
the roots of red clover. On the other hand, vetch, a commonly grown 
cover crop in California has been found to contain 89 per cent of its 
nitrogen in the tops and 11 per cent in the roots, soy beans, 93 per 
cent in the tops and 7 per cent in the roots, and cow peas, 84 per cent 
in the tops and 6 per cent in the roots. 

The benefit of utilizing both the tops and the roots of a legume 
as green manure is apparent. Feeding the legume as hay and re- 
turning the manure to the land, as in the case of feeding livestock, 
has certain advantages. Organic matter or humus under suitable 
conditions is attacked by micro-organisms which bring about de- 
composition and during the process carbonic acid and other acids 
are formed. These acids liberate the mineral matter in the soil and 
make it available as plant food. Thus three important elements, 
nitrogen, potassium, and phosphorus, are made available for the 
growth of the plant by the use of green manure. 


The amount of green vegetable matter produced above ground 
by the various legumes varies from ten to thirty tons per acre. A 
ton of green legume material may contain from ten to thirteen pounds 
of nitrogen, so the amount of nitrogen added to the soil may be from 
one hundred to four hundred pounds, according to the legume, and 
the tonnage of humus is subject to a similar variation. Taking 12 
cents as the commercial price for a pound of nitrogen and the growth 
from the Tangier peas as twenty tons of green stuff per acre we 
would be adding to the soil $24.00 worth of nitrogen to each acre by 
plowing under a crop of such peas. There is no cheaper method 
of applying nitrogen and humus to the soil than this. The cost of a 
ton of ordinary barnyard manure as bought and sold is many times 
that of a ton of green manure when we consider the expense of 
getting it incorporated with the soil. There is the added expense 
of hauling and distribution on the land. The same may be said of 
chopped alfalfa hay. Moreover, there is no certain method of stand- 
ardizing the value of these products. 



The benefit therefore of a good stand of the legume is evident. 
A firm rather than a loose seed bed is essential. To plow the land 
and sow the seed before the soil has settled is one of the most 
common causes of failure. Next in importance is the quality of 
the seed. If the seed is viable and has been certified, one can 
afford to pay a higher price, as much less seed per acre is required. 
It also eliminates any doubt as to whether the cause of failure can 
be attributed to the quality of the seed. Certified seed does not con- 
tain noxious weeds, which is another important item. 

Frequently there is a soil, especially sandy soil, that is so de- 
pleted of plant food that it is not capable of producing the first 
green-manure crop. Under these circumstances an application of 
superphosphate will give the legume the necessary encouragement. 
Spots in the field that have been scraped or are known to be non- 
productive should receive a light application of barnyard manure. 

Seeding should be done early in September or October for winter- 
growing crops so that the young plants can take advantage of the 
warm weather and make a good root growth before cold weather sets 
in. When well established the frost may check them, but not kill 
them, while if small and recently germinated it may destroy the 
small tender seedlings. Sometimes from one cause or another a good 
stand of a legume is not obtained the first time. There are in- 
stances where the first season produced only a few scattered plants, 
while a trial the following season with- the same legume produced a 
dense stand. The reasons have not always been apparent, but in- 
creased inoculation may have something to do with it. A thin stand 
the first time, provided the plants have nodules, will provide ample 
inoculation of the soil for the second season's crop. 


The selection of the legume to be grown will depend on local moist- 
ure, soil, and climatic conditions. In the northeastern counties where 
the climate will not permit of growing a crop in winter, spring sowing 
must be practiced. Red clover, sweet clover, hubam clover, alsike 
clover, alfalfa, field peas and hairy vetch will probably be found the 
most satisfactory for this purpose. 


In general, coarse heavy-stemmed legumes will produce the most 
organic matter where there are facilities for irrigation to supply 
ample moisture to aid in the decomposition of the material that 
is turned under. Such legumes as the small-seeded horse bean, the 
Tangier pea, cowpeas, and soy beans are of this nature. The former 
are winter-growing and the two latter summer-growing legumes. 
Legumes producing a finer leaf and stem growth than these are the 
common, hairy, woolly-podded and purple vetches and the monanthos 
lentil or vetch. These should be utilized in sections of the state 
that have to depend upon the natural precipitation for the moisture 

The following lists of legumes are recommended as green manure 

crops for California: 

Winter-growing Sandy Soil 

Hubam Clover . Bitter Clover 

Bitter Clover Hairy Vetch 

Bur-clover Bur-clover 

Garbanzos (Cicer) Lupines 

Small-seeded Horse Beans Peanuts 

Tangier Pea Cowpeas 

Fenugreek Soy Beans 
Hairy Vetch 

Purple Vetch Alkali Tolerant 
Woolly-podded Vetch 

Monanthos Lentil ? erS ?^ C1 ° Ver 

Lupines Sweet Clover 

r Hubam Clover 

Summer-growing Alfalfa 

_ Hairy Vetch 

Cowpeas Horse Beans 

Velvet Beans 

5? y Be T? nS Heavy Soil 

Mung Beans J 

Tepary Beans Peas 

Berseem Clover Tangier Pea 

Peanuts Horse Beans 

Alfalfa Mung Beans 

Sesbania Sesbania 

Moth Bean Fenugreek 

Knowledge of legumes has increased very materially in the last 
ten years. The University of California with its different agencies 
has been alive to the problem, and the work of Webber and Mertz 
of the Citrus Experiment Station at Riverside is particularly note- 
worthy. Trial legume gardens are supervised by the writer at Berke- 
ley, the Kearney Experiment Station, Fresno, and the Imperial 
Valley Experiment Station, El Centro. From these it is determined 
what varieties seem to be the most promising and they are grown for 
further experimentation. The following counties are actively coop- 
erating with the Agricultural Extension Service of the University 


in trials and demonstrations with legumes : Fresno, Glenn, Humboldt, 
Imperial, Kern, Kings, Los Angeles, Merced, Napa, Santa Barbara, 
San Benito, Sonoma, Stanislaus, Sutter, Tulare, and Yuba. 

Among the laymen we have P. A. Ingvason who has done much 
to introduce and make available a number of important new legumes. 
A. F. Etters, 0. E. Lambert, F. P. Bell, C. S. Milliken and L. A. Clark 
are others whose work with legumes will make its mark on the in- 
creased fertility and production of California soils. 

Some of the newer legumes are the Tangier pea, the monanthos 
vetch or lentil, the woolly-podded, Hungarian, and bitter vetches, 
sesbania, mung beans, the small-seeded horse bean, and the moth 
bean. These have proved valuable under experimentation and will 
soon be known and recognized as commercial legumes. 

Every encouragement should be given growers in the legume 
field as it means much to the continued prosperity of California